Image forming apparatuses include, for example, a printer, a facsimile machine, a copier, a plotter, and a multifunctional machine combining several of the functions of these apparatuses. As an image forming apparatus using a liquid discharge recording method that uses a recording head that discharges ink liquid droplets, for example, an inkjet recording apparatus is known.
Image forming apparatuses using the liquid discharge recording method perform image formation (hereinafter used as a synonym for recording, imaging, and printing) by discharging the ink droplets from the recording head onto a sheet being conveyed. Herein, such sheet is not limited to paper but includes any material to which the ink droplets and other liquids can adhere, such as an OHP (overhead projector) sheet, and is referred to also as a recorded medium, a recording medium, recording paper, a recording sheet, and so forth.
Image forming apparatuses using the liquid discharge recording method can be divided into serial-type image forming apparatuses, which form an image by discharging liquid droplets from a recording head that moves in a main scanning direction, and line-type image forming apparatuses, which form an image by using a line-type recording head that discharges liquid droplets while the head remains stationary.
As an example of the image forming apparatus as described above, a line-type image forming apparatus is known, as described above, which includes a line-type recording head including nozzle arrays arranged to cover the full width of the sheet being conveyed. The line-type recording head used in this case includes, for example, a plurality of short heads that themselves include arrays of nozzles for discharging liquid droplets, and which are arranged in the nozzle arrangement direction. This type of recording head is referred to as a multiple array head.
In the multiple array head as described above, ink is supplied to the plurality of heads. For example, there is a background apparatus that includes at least one head module group formed by a plurality of head modules each including a multiple array head and arranged in a direction substantially perpendicular to the sheet conveyance direction, and which has an ink channel for supplying ink to the head modules.
There is another background apparatus configured such that a common ink channel for supplying ink to the respective heads is provided between two groups of head modules arranged in a staggered manner.
Further, for easier replacement of the line-type recording head, still another background apparatus is configured to include an attachment member for attaching a head retaining member, which retains a recording module including at least a line head formed by a plurality of recording heads or by a single long recording head, such that the head retaining member can move in the sheet width direction perpendicular to the sheet conveyance direction from a storage position at which image recording is performed to a non-storage position at which image recording is not performed.
As described above, to form a line head by using a head module formed by a multiple array head in which a plurality of heads are arranged, it is common to form one head module by arranging the plurality of heads in two staggered arrays to discharge one line of liquid droplets of the same color.
Further, to form a color image, four head modules for discharging liquid droplets of respective colors of Y (yellow), M (magenta), C (cyan), and K (black), for example, may be arranged in the sheet conveyance direction, or heads corresponding to four colors may be arranged on a base member to form one head module.
In any of the configurations described above, there are at least two arrays of heads (i.e., head arrays) for discharging the liquid droplets of the same color in the sheet conveyance direction. Further, to improve the accuracy of the landing position of liquid droplets of any given color, and to improve the accuracy of the landing position of liquid droplets of different colors, it is desired to make the overall distance in the sheet conveyance direction as short as possible. For example, in a configuration including four head modules arranged in the sheet conveyance direction and each including two staggered head arrays to discharge one line of liquid droplets of one color, it is desired to reduce the intervals between the head modules.
In this case, if eight head arrays for four colors are arranged on a plate-like base member as described above, the base member of the simple plate shape needs to have openings through which ink droplets are discharged from the heads onto a sheet. Due to the limited strength of the base member, therefore, there is a limitation in reducing the intervals between the head arrays. Accordingly, it is difficult to reduce the size of the entire recording head.
Further, in the background line head, the ink supply channel and a board for transmitting signals to the heads are provided between the head arrays in the horizontal direction with respect to the heads. Therefore, it is difficult to reduce the intervals between the head arrays, and the entire line head is increased in size.
Further, in the multiple array head, it is difficult to separately replace the heads. Therefore, an easier head replacement operation is desired.